This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Bacterial Multicomponent Monooxygenases (BMMs) such as methane monooxygenase (MMO), toluene/o-xylene monooxygenase (ToMO), and phenol hydroxylase (PH) catalyze the regio- and enantioselective oxidation of saturated and aromatic hydrocarbons to yield alcohols, phenols, catechols, and epoxides. Regulatory and reductase protein components are required to effect catalysis in BMM hydroxylases, which contain carboxylate-bridged non-heme diiron active sites where the oxidation reactions occur at a dioxygen-activated intermediate. Structures of the MMO hydroxylase in complex with the regulatory protein MMOB and the related inhibitory protein MMOD, together with MMOH-O2 intermediates, are sought to probe component interactions and reactive pathways in the MMO system. Structures of component protein complexes, oxygenated intermediates, and the diiron(II) reduced, metal-reconstituted, and mutant forms of ToMO and PH hydroxylases and their complexes will similarly be pursued.